The present invention relates generally to printers, and more particularly to a printer assembly which provides tension for the idler pulley.
Printers include those printers having a printhead which is moved by a carrier belt across a page during the printing process. The carrier belt is positioned around and between two pulleys, wherein one of the pulleys is a drive pulley and the other of the pulleys is an idler pulley. Typically, the carrier belt has teeth which engage matching teeth on the pulleys. During the life of the printer, the carrier belt will increase in length through wear and lead to printing problems. One solution has been to provide a spring-biased mechanism to maintain tension on the idler pulley as the length of the carrier belt increases.
In one known printer, a leaf spring pulls the idler pulley away from the motor pulley to maintain tension on the carrier belt despite the belt increasing in length through wear. At the same time, a toothed wedge, biased by a second spring, acts as a hard stop preventing the idler pulley from moving inboard toward the motor pulley which can cause the motor pulley to skip teeth on the carrier belt (or slip if the carrier belt has no teeth) leading to printing errors. The leaf spring, the toothed wedge, and the second spring are located outboard of the idler pulley. This outboard arrangement adds to the dimensions of a printer assembly which includes the motor and idler pulleys and the spring-biased mechanism which maintains tension on the idler pulley.
In another known printer, an inboard-extending spring rotates an inboard toothless cam which pushes a guide pulley away from a drive pulley to maintain tension on the cable despite the cable increasing in length through wear. The spring-biased cam does not provide a hard stop for the guide pulley from moving toward the drive pulley. Inboard movement of the guide pulley toward the drive pulley can cause the drive pulley to skip teeth on the cable (or slip if the cable has no teeth) which can lead to printing errors.
What is needed is a compact printer assembly which provides tension for the idler pulley supporting the printhead carrier belt and which provides a hard stop preventing the idler pulley from moving in an inboard direction.
A broad expression of diverse embodiments of the invention is for a printer assembly including an idler pulley, a printhead carrier belt, an idler-pulley spring, and a ratchet stop. The printhead carrier belt is operatively connected to the idler pulley and extends in an inboard direction from the idler pulley. The idler-pulley spring biases the idler pulley in an outboard direction substantially opposite to the inboard direction. The ratchet stop is positioned inboard of the idler pulley and operatively engages the idler pulley against movement of the idler pulley in the inboard direction.
A first embodiment of the invention is for a printer assembly including an idler pulley, a printhead carrier belt, an idler-pulley spring, a printer housing, an idler-pulley frame, and a ratchet stop. The printhead carrier belt is operatively connected to the idler pulley and extends in an inboard direction from the idler pulley. The idler-pulley spring biases the idler pulley in an outboard direction substantially opposite to the inboard direction. The idler-pulley frame rotatably supports the idler pulley and is movably attached to the printer housing for inboard and outboard movement with respect to the printer housing. The ratchet stop is positioned inboard of the idler pulley. The ratchet stop includes substantially-inboard-facing ratchet teeth and a ratchet pawl. The ratchet teeth are attached to the idler-pulley frame. The ratchet pawl is pivotally attached to the printer housing and is operatively engaged with one of the ratchet teeth.
A second embodiment of the invention is for a printer assembly including an idler pulley, a printhead carrier belt, an idler-pulley spring, a printer housing, an idler-pulley frame, and a ratchet stop. The printhead carrier belt is operatively connected to the idler pulley and extends in an inboard direction from the idler pulley. The idler-pulley spring biases the idler pulley in an outboard direction substantially opposite to the inboard direction. The idler-pulley frame rotatably supports the idler pulley and is movably attached to the printer housing for inboard and outboard movement with respect to the printer housing. The ratchet stop is positioned inboard of the idler pulley. The ratchet stop includes a ratchet cam and a ratchet spring. The ratchet cam is rotatably attached to the printer housing and operatively engages the idler-pulley frame. The ratchet spring is attached to the ratchet cam and to the printer housing and is aligned substantially perpendicular to the inboard direction.
Several benefits and advantages are derived from the invention. Applicant""s idler-pulley spring maintains tension on the idler pulley despite lengthening of the carrier belt from wear. Applicant""s ratchet stop provides a hard stop preventing inboard movement of the idler pulley which can lead to printing errors. Applicant""s ratchet stop (and preferably idler-pulley spring) is located inboard of the idler pulley to minimize the dimensions of the printer assembly.